Vertical transport fets having a gradient threshold voltage

ABSTRACT

Vertical transport field effect transistors (FETs) having improved device performance are provided. Notably, vertical transport FETs having a gradient threshold voltage are provided. The gradient threshold voltage is provided by introducing a threshold voltage modifying dopant into a physically exposed portion of a metal gate layer composed of an n-type workfunction TiN. The threshold voltage modifying dopant changes the threshold voltage of the original metal gate layer.

BACKGROUND

The present application relates to a semiconductor structure and amethod of forming the same. More particularly, the present applicationrelates to a semiconductor structure including vertical transport fieldeffect transistors having improved device performance as well as amethod of forming such a structure.

Conventional vertical transistors are devices where the source-draincurrent flows in a direction normal to the substrate surface. In suchdevices, a vertical semiconductor pillar (or fin) defines the channelwith the source and drain located at opposing ends of the semiconductorpillar. Vertical transistors are an attractive option for technologyscaling for 5 nm and beyond.

The lateral asymmetric channel (LAC) doping profile approach providesone of the most effective ways to improve the electrical characteristicsof transistor devices. For LAC devices, the doping concentration of thesource side is higher than that of the drain side in the channel. Thechannel potential transition at the source side channel region is muchstepper than that of the other channel regions, while the device isoperating due to non-uniform channel doping. Such a steep potentialdistribution near the source side enhances the lateral channel electricfield and this increases the carrier mobility. This approach, however,suffers from channel dopant diffusion and dopant variation. Also, it isdifficult to design short channel devices using the LAC approach.

There is thus a need for providing vertical transport field effecttransistors (FETs) having improved electrical characteristics and deviceperformance.

SUMMARY

Vertical transport field effect transistors (FETs) having improveddevice performance are provided. Notably, vertical transport FETs havinga gradient threshold voltage are provided. The gradient thresholdvoltage is provided by introducing a threshold voltage modifying dopantinto a physically exposed portion of a metal gate layer composed of ann-type workfunction TiN. The threshold voltage modifying dopant changesthe threshold voltage of the original metal gate layer.

One aspect of the present application relates to a semiconductorstructure. In one embodiment the semiconductor structure includes atleast one semiconductor fin present in a device region and extendingupwards from a surface a base semiconductor substrate. A bottomsource/drain structure is located on the base semiconductor substrateand contacts sidewall surfaces of a lower portion of the at least onesemiconductor fin. The bottom source/drain structure serves as a drainregion. A gate dielectric layer is located above the bottom source/drainstructure and contacts another portion of the sidewall surfaces of theat least one semiconductor fin. A gate structure is located laterallyadjacent a sidewall of the gate dielectric layer, the gate structureincludes a TiN liner having a first threshold voltage and a TiN portionhaving a second threshold voltage that is greater than the firstthreshold voltage. A top source/drain structure is located on an upperportion of the at least one semiconductor fin and serving a sourceregion.

In another embodiment, the semiconductor structure includes a verticaltransport nFET and a laterally adjacent vertical transport pFET. In sucha structure, the vertical transport nFET includes at least onesemiconductor fin present in an nFET device region and extending upwardsfrom a surface of a base semiconductor substrate. A bottom n-dopedsource/drain structure is located on the base semiconductor substrateand contacts sidewall surfaces of a lower portion of the at least onesemiconductor fin, wherein the bottom n-doped source/drain structureserves as a drain region. A gate dielectric layer is located above thebottom n-doped source/drain structure and contacts another portion ofthe sidewall surfaces of the at least one semiconductor fin. An nFETgate structure is located laterally adjacent a sidewall of the gatedielectric layer, the nFET gate structure comprises a TiN liner having afirst threshold voltage and a TiN portion having a second thresholdvoltage that is greater than the first threshold voltage. A top n-dopedsource/drain structure is located on an upper portion of the at leastone semiconductor fin and serves as a source region.

The vertical transport pFET of such a structure includes at least onesemiconductor fin present in a pFET device region and extending upwardsfrom the surface of the base semiconductor substrate. A bottom p-dopedsource/drain structure is located on the base semiconductor substrateand contacts sidewall surfaces of a lower portion of the at least onesemiconductor fin, wherein the bottom p-doped source/drain structureserves as a drain region. A gate dielectric layer is located above thebottom p-doped source/drain structure and contacting another portion ofthe sidewall surfaces of the at least one semiconductor fin. A pFET gatestructure is located laterally adjacent a sidewall of the gatedielectric layer, the pFET gate structure comprising a TiN liner havingthe second threshold voltage and a TiN portion having a third thresholdvoltage that is greater than the second threshold voltage. A top p-dopedsource/drain structure is located on an upper portion of the at leastone semiconductor fin and serves as a source region.

Another aspect of the present application relates to a method of forminga semiconductor structure. In one embodiment, the method may includeproviding at least one semiconductor fin extending upwards from asurface of a base semiconductor substrate and located in a deviceregion, wherein the at least one semiconductor fin contains a hard maskcap thereon. A bottom source/drain structure is then formed on the basesemiconductor substrate and contacting sidewall surfaces of a lowerportion of the at least one semiconductor fin. Next, a gate dielectricmaterial layer is formed above the bottom source/drain structure andcontacting physically exposed portions of the at least one semiconductorfin and the hard mask cap. An n-workfucntion TiN layer having a firstthreshold voltage is formed on the gate dielectric material layer. Ablock mask is then formed over a lower portion of the n-workfucntion TiNlayer. Next, physically exposed portions of the n-workfunction TiN layerare modified by incorporating a threshold voltage modifying dopanttherein to provide a modified TiN layer having a second thresholdvoltage that is greater than the first threshold voltage. Next, theblock mask is recessed to physically expose a portion, but not anentirety, of the modified TiN layer, and then the physically exposedportions of the modified TiN layer and the underlying gate dielectricmaterial layer are removed to expose an upper portion of the at leastone semiconductor fin. Next, the recessed block mask and the hard maskare removed, and thereafter a top source/drain structure is formed fromphysically exposed sidewall surfaces and a topmost surface of the atleast one semiconductor fin.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross sectional view of an exemplary semiconductor structureof the present application during an early stage of fabrication andincluding a hard mask layer located on a surface of a semiconductorsubstrate.

FIG. 2 is a cross sectional view of the exemplary semiconductorstructure of FIG. 1 after patterning the hard mask layer and an uppersemiconductor material portion of the semiconductor substrate to providea plurality of hard mask capped semiconductor fins extending upwardsfrom a surface of a remaining portion of the semiconductor substrate.

FIG. 3 is a cross sectional view of the exemplary semiconductorstructure of FIG. 2 after forming a bottom n-doped source/drainstructure in an nFET device and a bottom p-doped source/drain structurein a pFET device region, and forming an isolation structure between thedifferent device regions.

FIG. 4 is a cross sectional view of the exemplary semiconductorstructure of FIG. 3 after forming a bottom spacer on a physicallyexposed surface of the bottom source/drain structures in each of thedevice regions.

FIG. 5 is a cross sectional view of the exemplary semiconductorstructure of FIG. 4 after forming a gate dielectric material layer andan n-type workfunction TiN layer.

FIG. 6 is a cross sectional view of the exemplary semiconductorstructure of FIG. 5 after forming a block mask in the nFET deviceregion.

FIG. 7 is a cross sectional view of the exemplary semiconductorstructure of FIG. 6 after performing a first metal gate treatment on thephysically exposed portions of the n-type workfunction TiN layer in thenFET device region and the pFET device region to provide a firstmodified TiN layer in both device regions.

FIG. 8 is a cross sectional view of the exemplary semiconductorstructure of FIG. 7 after forming additional block mask material,patterning the additional block mask material to provide a second blockmask and performing a second metal gate treatment on the physicallyexposed first modified TiN layer in the pFET device region so as toprovide a second modified TiN layer.

FIG. 9 is a cross sectional view of the exemplary semiconductorstructure of FIG. 8 after recessing the second block mask, removingphysically exposed portions of the first modified TiN layer in the nFETdevice region and physically exposed portions of the second modified TiNlayer in the pFET device region, and removing the gate dielectricmaterial layer that is located beneath the physically exposed portionsof the first modified TiN layer and the physically exposed portions ofthe second modified TiN layer.

FIG. 10 is a cross sectional view of the exemplary semiconductorstructure of FIG. 9 after removing the recessed second block mask andforming a gate encapsulation layer.

FIG. 11 is a cross sectional view of the exemplary semiconductorstructure of FIG. 10 after forming a middle-of-the-line (MOL) dielectricmaterial.

FIG. 12 is a cross sectional view the exemplary semiconductor structureof FIG. 11 after physically exposing an uppermost portion of eachsemiconductor fin in the nFET device region and the pFET device region,and forming a top n-doped source/drain structure on the physicallyexposed surfaces of the semiconductor fins in the nFET device region anda top p-doped source/drain structure on the physically exposed surfacesthe semiconductor fins in the pFET device region.

FIG. 13 is a cross sectional view of the exemplary semiconductorstructure of FIG. 12 after forming a top spacer and top source/draincontact structures.

DETAILED DESCRIPTION

The present application will now be described in greater detail byreferring to the following discussion and drawings that accompany thepresent application. It is noted that the drawings of the presentapplication are provided for illustrative purposes only and, as such,the drawings are not drawn to scale. It is also noted that like andcorresponding elements are referred to by like reference numerals.

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide an understanding ofthe various embodiments of the present application. However, it will beappreciated by one of ordinary skill in the art that the variousembodiments of the present application may be practiced without thesespecific details. In other instances, well-known structures orprocessing steps have not been described in detail in order to avoidobscuring the present application.

It will be understood that when an element as a layer, region orsubstrate is referred to as being “on” or “over” another element, it canbe directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “beneath” or “under” another element, it can bedirectly beneath or under the other element, or intervening elements maybe present. In contrast, when an element is referred to as being“directly beneath” or “directly under” another element, there are nointervening elements present.

Referring first to FIG. 1, there is illustrated an exemplarysemiconductor structure of the present application during an early stageof fabrication. The exemplary semiconductor structure of FIG. 1 includesa hard mask layer 14L located on a surface of a semiconductor substrate10.

The semiconductor substrate 10 that can be employed in the presentapplication is a bulk semiconductor substrate. By “bulk” it is meantthat the semiconductor substrate 10 is entirely composed of at least onesemiconductor material having semiconducting properties. Examples ofsemiconductor materials that may provide the semiconductor substrate 10include silicon (Si), germanium (Ge), silicon germanium alloys (SiGe),silicon carbide (SiC), silicon germanium carbide (SiGeC), III-V compoundsemiconductors or II-VI compound semiconductors. III-V compoundsemiconductors are materials that include at least one element fromGroup III of the Periodic Table of Elements and at least one elementfrom Group V of the Periodic Table of Elements. II-VI compoundsemiconductors are materials that include at least one element fromGroup II of the Periodic Table of Elements and at least one element fromGroup VI of the Periodic Table of Elements. In one example, thesemiconductor substrate 10 may be entirely composed of silicon. In someembodiments, the semiconductor substrate 10 may include a multilayeredsemiconductor material stack including at least two differentsemiconductor materials, as defined above. In one example, themultilayered semiconductor material stack may comprise, in any order, astack of Si and a silicon germanium alloy.

The semiconductor material that provides the semiconductor substrate 10may be a single crystalline semiconductor material. The semiconductormaterial that provides the semiconductor substrate 10 may have any ofthe well known crystal orientations. For example, the crystalorientation of the semiconductor substrate 10 may be {100}, {110}, or{111}. Other crystallographic orientations besides those specificallymentioned can also be used in the present application.

The hard mask layer 14L that can be used in the present applicationincludes any dielectric hard mask material such as, for example, silicondioxide, silicon nitride and/or silicon oxynitride. In one example,silicon nitride is employed as the dielectric hard mask material. Thehard mask layer 14L may be formed utilizing a deposition process suchas, for example, chemical vapor deposition (CVD) or plasma enhancedchemical vapor deposition (PECVD). In some embodiments, the hard masklayer 14L may be formed by a thermal growth process such as, forexample, thermal oxidation and/or thermal nitridation. In yet otherembodiments, the hard mask layer 14L may be formed utilizing acombination of, and in any order, a deposition process and a thermalgrowth process. The hard mask layer 14L is a continuous layer (withoutany breaks or gaps) whose thickness may be from 20 nm to 100 nm. Otherthicknesses that are lesser than, or greater than the aforementionedthicknesses values may also be employed as the thickness of the hardmask layer 14L.

Referring now to FIG. 2, there is illustrated the exemplarysemiconductor structure of FIG. 1 after patterning the hard mask layer14L and an upper semiconductor material portion of the semiconductorsubstrate 10 to provide a plurality of hard mask capped semiconductorfins extending upwards from a surface of a remaining portion of thesemiconductor substrate 10. Each hard mask cap 14 that is formedconstitutes a remaining, non-etched portion of the hard mask layer 14L.Each semiconductor fin 10F constitutes a remaining, non-etched uppersemiconductor portion of the semiconductor substrate 10 which is presentdirectly beneath one of the hard mask caps 14. The remaining portion ofthe semiconductor substrate 10 that is located beneath each of thesemiconductor fins 10F may be referred to herein as a base semiconductorsubstrate 10B.

In some embodiments, the semiconductor fins 10F and the basesemiconductor substrate 10B may be composed of a same semiconductormaterial. In other embodiments, the semiconductor fins 10F and the basesemiconductor substrate 10B may be composed of different semiconductormaterials.

The number of hard mask capped semiconductor fins that are formed mayvary and can be predetermined prior to forming the same. For example, itis possible to form a single hard mask capped semiconductor fin. As isshown, each semiconductor fin 10F contains a hard mask cap 14 whosesidewall surfaces are vertically aligned with the sidewall surfaces ofone of the semiconductor fin 10F.

In one embodiment, the patterning of the hard mask layer 14L and thesemiconductor substrate 10 may include lithography and etching. Thelithographic process includes forming a photoresist (not shown) atop amaterial or material stack to be patterned, exposing the photoresist toa desired pattern of radiation, and developing the exposed photoresistutilizing a conventional resist developer. The photoresist may be apositive-tone photoresist, a negative-tone photoresist or a hybrid-tonephotoresist. The etching process (i.e., patterned transfer etch)includes a dry etching process (such as, for example, reactive ionetching, ion beam etching, plasma etching or laser ablation), and/or awet chemical etching process. In some embodiments, the patternedphotoresist is removed from the structure immediately after the patternhas been transferred into the hard mask layer 14L. In other embodiments,the patterned photoresist is removed from the structure after thepattern has been transferred into both the hard mask layer 14L and thesemiconductor substrate 10. In either embodiment, the patternedphotoresist may be removed utilizing a conventional photoresiststripping process such as, for example, ashing.

In another embodiment, the patterning of the hard mask layer 14L and thesemiconductor substrate 10 may include a sidewall image transfer (SIT)process. The SIT process includes forming a mandrel material layer (notshown) atop the material or material layers that are to be patterned.The mandrel material layer (not shown) can include any material(semiconductor, dielectric or conductive) that can be selectivelyremoved from the structure during a subsequently performed etchingprocess. In one embodiment, the mandrel material layer (not shown) maybe composed of amorphous silicon or polysilicon. In another embodiment,the mandrel material layer (not shown) may be composed of a metal suchas, for example, Al, W, or Cu. The mandrel material layer (not shown)can be formed, for example, by chemical vapor deposition or plasmaenhanced chemical vapor deposition. Following deposition of the mandrelmaterial layer (not shown), the mandrel material layer (not shown) canbe patterned by lithography and etching to form a plurality of mandrelstructures (also not shown) on the topmost surface of the structure.

The SIT process continues by forming a spacer (not shown) on eachsidewall of each mandrel structure. The spacer can be formed bydeposition of a spacer material and then etching the deposited spacermaterial. The spacer material may comprise any material having an etchselectivity that differs from the mandrel material. Examples ofdeposition processes that can be used in providing the spacer materialinclude, for example, chemical vapor deposition (CVD), plasma enhancedchemical vapor deposition (PECVD), or atomic layer deposition (ALD).Examples of etching that be used in providing the spacers include anyetching process such as, for example, reactive ion etching.

After formation of the spacers, the SIT process continues by removingeach mandrel structure. Each mandrel structure can be removed by anetching process that is selective for removing the mandrel material.Following the mandrel structure removal, the SIT process continues bytransferring the pattern provided by the spacers into the underlyingmaterial or material layers. The pattern transfer may be achieved byutilizing at least one etching process. Examples of etching processesthat can used to transfer the pattern may include dry etching (i.e.,reactive ion etching, plasma etching, and ion beam etching or laserablation) and/or a chemical wet etch process. In one example, the etchprocess used to transfer the pattern may include one or more reactiveion etching steps. Upon completion of the pattern transfer, the SITprocess concludes by removing the spacers from the structure. Eachspacer may be removed by etching or a planarization process.

In yet a further embodiment, the patterning of the hard mask layer 14Land the semiconductor substrate 10 may include a direct self-assembly(DSA) process in which a copolymer that is capable of directself-assembly is used.

As used herein, a “semiconductor fin” refers to a semiconductor materialthat includes a pair of vertical sidewalls that are parallel to eachother. As used herein, a surface is “vertical” if there exists avertical plane from which the surface does not deviate by more thanthree times the root mean square roughness of the surface. In oneembodiment, each semiconductor fin 10F has a height from 20 nm to 200nm, and a width from 5 nm to 30 nm. Other heights and/or widths that arelesser than, or greater than, the ranges mentioned herein can also beused in the present application. Each semiconductor fin 10F is spacedapart from its nearest neighboring semiconductor fin 10F by a pitch offrom 20 nm to 100 nm; the pitch is measured from one point of onesemiconductor fin to the exact point on a neighboring semiconductor fin.Also, each semiconductor fin 10F is oriented parallel to each other. Anopening or gap is present between each neighboring pairs ofsemiconductor fins 10F.

Referring now to FIG. 3, there is illustrated the exemplarysemiconductor structure of FIG. 2 after forming a bottom n-dopedsource/drain structure 18 in an nFET device 100 and a bottom p-dopedsource/drain structure 20 in a pFET device region 102, and forming anisolation structure 16 between the different device regions (100/102).In some embodiments, only a single device region, nFET device region 100or pFET device region 102 can be formed.

The bottom n-doped source/drain structure 18 and the bottom p-dopedsource/drain structure 20 can be formed in any order. For example, andin one embodiment, the bottom n-doped source/drain structure 18 can beformed prior to the bottom p-doped source/drain structure 20. In such anembodiment, a block mask is formed in the pFET device region 102 andthen the bottom n-doped source/drain structure 18 is formed by anepitaxial deposition or growth process. Following the epitaxialdeposition or growth of the bottom n-doped source/drain structure 18,the block mask is removed from the pFET device region 102, another blockmask is formed in the nFET device region 100 that now includes thebottom n-doped source/drain structure 18, and thereafter the bottomp-doped source/drain structure 20 is formed by another epitaxialdeposition or growth process. Following epitaxial deposition or growthof the bottom p-doped source/drain structure 20, the another block maskis removed from the nFET device region 100. In embodiments in which thebottom p-doped source/drain structure 20 is formed prior to the bottomn-doped source/drain structure 18, the order of the above mentionedprocessing steps is reversed.

In the present application, the bottom n-doped source/drain structure 18and the bottom p-doped source/drain structure 20 are used as drainregions of the resultant vertical transport FETs.

The bottom n-doped source/drain structure 18 includes a semiconductormaterial and an n-type dopant. The semiconductor material that providesthe bottom nFET source/drain structure 18 may be the same as, ordifferent from, the semiconductor material of semiconductor substrate10. The term “n-type” refers to the addition of impurities thatcontributes free electrons to an intrinsic semiconductor. In a siliconcontaining semiconductor material, examples of n-type dopants, i.e.,impurities, include, but are not limited to, antimony, arsenic andphosphorous. The concentration of n-type dopant within the semiconductormaterial that provides the bottom n-doped source/drain structure 18 canrange from 1×10¹⁸ atoms/cm³ to 1×10²¹ atoms/cm³, although dopantconcentrations greater than 1×10²¹ atoms/cm³ or less than 1×10¹⁸atoms/cm³ are also conceived. The bottom n-doped source/drain structure18 has a height that is less than a height of each of the semiconductorfins 10F. The bottom n-doped source/drain structure 18 contacts sidewallsurfaces of a bottom portion of the semiconductor fins 10F in the nFETdevice region 100.

The bottom p-doped source/drain structure 20 includes a semiconductormaterial and a p-type dopant. The semiconductor material that providesthe bottom pFET source/drain structure 20 may be the same as, ordifferent from, the semiconductor material of semiconductor substrate10. Also, the semiconductor material that provides the bottom p-dopedsource/drain structure 20 may be the same as, or different from, thesemiconductor material that provides the bottom p-doped source/drainstructure 18. The term “p-type” refers to the addition of impurities toan intrinsic semiconductor that creates deficiencies of valenceelectrons. In a silicon-containing semiconductor material, examples ofp-type dopants, i.e., impurities, include, but are not limited to,boron, aluminum, gallium and indium. The concentration of p-type dopantwithin the semiconductor material that provides the bottom p-dopedsource/drain structure 20 can range from 1×10¹⁸ atoms/cm³ to 1×10²¹atoms/cm³, although dopant concentrations greater than 1×10²¹ atoms/cm³or less than 1×10¹⁸ atoms/cm³ are also conceived. The bottom p-dopedsource/drain structure 20 has a height that is less than a height ofeach of the semiconductor fins 10F. The bottom pFET source/rainstructure 20 contacts sidewall surface of a bottom portion of thesemiconductor fins 10F in the pFET device region 102. The bottom pFETsource/rain structure 20 may have a topmost surface that is coplanarwith a topmost surface of the bottom n-doped source/drain structure 18.

The bottom source/drain structures (18/20) can be formed utilizing anepitaxial growth (or deposition) process. The terms “epitaxially growingand/or depositing” and “epitaxially grown and/or deposited” mean thegrowth of a semiconductor material on a deposition surface of asemiconductor material, in which the semiconductor material being grownhas the same crystalline characteristics as the semiconductor materialof the deposition surface. In an epitaxial growth process, the chemicalreactants provided by the source gases are controlled and the systemparameters are set so that the depositing atoms arrive at the depositionsurface of the semiconductor substrate with sufficient energy to movearound on the surface and orient themselves to the crystal arrangementof the atoms of the deposition surface. Therefore, an epitaxialsemiconductor material has the same crystalline characteristics as thedeposition surface on which it is formed. In the present application,the bottom source/drain structures (18/20) have an epitaxialrelationship with the physically exposed surface of the basesemiconductor substrate 10B and the sidewalls of each semiconductor fin10F.

Examples of various epitaxial growth process apparatuses that can beemployed in the present application include, e.g., rapid thermalchemical vapor deposition (RTCVD), low-energy plasma deposition (LEPD),ultra-high vacuum chemical vapor deposition (UHVCVD), atmosphericpressure chemical vapor deposition (APCVD) and molecular beam epitaxy(MBE). The epitaxial growth may be performed at a temperature of from300° C. to 800° C. The epitaxial growth can be performed utilizing anywell known precursor gas or gas mixture. Carrier gases like hydrogen,nitrogen, helium and argon can be used. A dopant (n-type or p-type, asdefined below) is typically added to the precursor gas or gas mixture.

In some embodiments, isolation structure 16 can be formed between thedifferent device regions (100/102). The isolation structure 16 can beformed by forming a trench opening in an area in which sidewalls of thebottom source/drain structures (18/20) are in contact with each other,and then filling the trench opening with a trench dielectric materialsuch as, for example, silicon dioxide. A recess etch may follow thetrench filling step. Although the present application describes formingthe isolation structure 16 after forming the bottom source/drainstructures (18/20), the isolation structure 16 may be formed prior toforming the bottom source/drain structures (18/20).

Referring now to FIG. 4, there is illustrated the exemplarysemiconductor structure of FIG. 3 after forming a bottom spacer 22 on aphysically exposed surface of the bottom source/drain structures (18/20)in each of the device regions (100/102).

The bottom spacer 22 contacts sidewall surfaces of the lower portion ofthe semiconductor fins 10F present in each of the device regions(100/102). The bottom spacer 22 may be composed of any dielectric spacermaterial including for example, silicon dioxide, silicon nitride orsilicon oxynitride. The bottom spacer 22 may be formed utilizing adeposition process such as, for example, chemical vapor deposition orplasma enhanced chemical vapor deposition. In some instances, an etchback process may follow the deposition of the dielectric spacer materialthat provides the bottom spacer 22. The bottom spacer 22 may have athickness from 4 nm to 10 nm. Other thicknesses that are lesser than, orgreater than, the aforementioned thickness range may also be employed inthe present application as the thickness of the bottom spacer 22 as longas the height of the bottom spacer 22 is not greater than the height ofthe semiconductor fins 10F and there is sufficient area on each thesemiconductor fins 10F to form other components of a vertical transportFET.

Referring now to FIG. 5, there is illustrated the exemplarysemiconductor structure of FIG. 4 after forming a gate dielectricmaterial layer 24 and an n-type workfunction TiN layer 26. In thepresent application, the gate dielectric material layer 24 is formed onexposed surfaces of the bottom spacer 22, and the semiconductor fins 10Fand the hard mask caps 14 that are present in both device regions(100/102). The n-type workfunction TiN layer 26 is formed on the gatedielectric material layer 24. The n-type workfunction TiN layer 26 maybe referred to as a metal gate layer.

The gate dielectric material layer 24 may be composed of a gatedielectric material such as, for example, an oxide, nitride, and/oroxynitride. In one example, the gate dielectric material layer 24 can bea high-k material having a dielectric constant greater than silicondioxide. Exemplary high-k dielectrics include, but are not limited to,HfO₂, ZrO₂, La₂O₃, Al₂O₃, TiO₂, SrTiO₃, LaAlO₃, Y₂O₃, HfO_(x)N_(y),ZrO_(x)N_(y), La₂O_(x)N_(y), Al₂O_(x)N_(y), TiO_(x)N_(y),SrTiO_(x)N_(y), LaAlO_(x)N_(y), Y₂O_(x)N_(y), SiON, SiN_(x), a silicatethereof, and an alloy thereof. Each value of x is independently from 0.5to 3 and each value of y is independently from 0 to 2. In someembodiments, a multilayered gate dielectric structure comprisingdifferent gate dielectric materials, e.g., silicon dioxide, and a high-kgate dielectric, can be formed and used as gate dielectric materiallayer 24. The gate dielectric material that provides the gate dielectricmaterial layer 24 can be formed by any deposition process including, forexample, chemical vapor deposition (CVD), plasma enhanced chemical vapordeposition (PECVD), physical vapor deposition (PVD), sputtering, oratomic layer deposition (ALD). In one embodiment of the presentapplication, the gate dielectric material that provides the gatedielectric material layer 24 can have a thickness in a range from 1 nmto 10 nm. Other thicknesses that are lesser than, or greater than, theaforementioned thickness range can also be employed for the gatedielectric material that provides the gate dielectric material layer 24.

The n-type workfunction TiN layer 26 that is formed at this point of thepresent application has a first workfunction value which is typically ina range from 4.3 eV to 4.6 eV. In accordance with the presentapplication, the n-type workfunction TiN layer 26 has a first thresholdvoltage.

The n-type workfunction TiN layer 26 can be formed by a depositing a TiNlayer and thereafter annealing the TiN layer. The depositing may includechemical vapor deposition (CVD), plasma enhanced chemical vapordeposition (PECVD) or atomic layer deposition (ALD). The anneal used toprovide the n-type workfunction TiN layer 26 may be a furnace anneal ora laser anneal. The anneal may be performed at a temperature from 800°C. to 1100° C. and in an inert ambient such as, for example, helium,argon and/or neon.

In one embodiment of the present application, the n-type workfunctionTiN layer 26 can have a thickness in a range from 5 nm to 20 nm. Otherthicknesses that are lesser than, or greater than, the aforementionedthickness range can also be employed for the gate dielectric materialthat provides the n-type workfunction TiN layer 26.

Referring now to FIG. 6, there is illustrated the exemplarysemiconductor structure of FIG. 5 after forming a block mask 28 in thenFET device region 100. Block mask 28 is designed to protect a lowerportion of the n-type workfunction TiN layer 26 in the nFET deviceregion 100, while leaving an upper portion of the n-type workfunctionTiN layer 26 in the nFET device region 100 physically exposed. The blockmask 28 also leaves the entirety of the n-type workfunction TiN layer 26in the pFET device region 102 physically exposed.

Block mask 28 may be composed of any block mask material such as, forexample, an organic planarization material. The organic planarizationmaterial can be a self-planarizing organic material that includescarbon, hydrogen, oxygen, and optionally nitrogen, fluorine, andsilicon. In one embodiment, the self-planarizing organic material can bea polymer with sufficiently low viscosity so that the top surface of theapplied polymer forms a planar horizontal surface. In one embodiment,the organic planarization material can include a transparent organicpolymer. The organic planarization material can be a standard C_(x)H_(y)polymer.

Block mask 28 may be formed by deposition of the block mask material andthen patterning the deposited block mask material. The patterning of theblock mask material may be performed by lithography and etching. In someembodiments, and following the patterning process, the patterned blockmask may be recessed to provide block mask 28.

Referring now to FIG. 7, there is illustrated the exemplarysemiconductor structure of FIG. 6 after performing a first metal gatetreatment on the physically exposed portions of the n-type workfunctionTiN layer 26 in the nFET device region 100 and the pFET device region102 to provide a first modified TiN layer 30 in both device regions(100/102). The first modified TiN layer 30 has a second workfunctionvalue that is higher than the first workfunction value. In oneembodiment, the second workfunction value of the first modified TiNlayer 30 is from 4.6 eV to 4.9 eV. In accordance with the presentapplication, the first modified TiN layer 30 has a second thresholdvoltage that is higher, i.e., greater, than the first threshold voltage.

The first metal gate treatment includes introducing a threshold voltagemodifying dopant such as, for example, fluorine or oxygen into thephysically exposed portions of the n-type workfunction TiN layer 26 inthe nFET device region 100 and the pFET device region 102. The thresholdvoltage modifying dopant may be introduced into the physically exposedportions of the n-type workfunction TiN layer 26 in the nFET deviceregion 100 and the pFET device region 102 utilizing a gas phase dopantprocess. The block mask 28 prevents introduction of the thresholdvoltage modifying dopant into portions of the n-type workfunction TiNlayer 26 that are covered/protected by the block mask 28. The remainingn-type workfunction TiN layer 26 that is located beneath the block mask28 may be referred to as an n-type workfunction TiN liner 26L.

In some embodiments, the concentration of threshold voltage modifyingdopant that is present in the first modified TiN layer 30 can be from1.5E20 atoms/cm³ to 8E21 atoms/cm³. Other concentrations of thresholdvoltage modifying dopant besides the range mentioned herein can bepresent in the first modified TiN layer 30 so as long as theconcentration of the threshold voltage modifying dopant that is presentin the first modified TiN layer 30 provides the desired thresholdvoltage change in both device regions.

Referring now to FIG. 8, there is illustrated the exemplarysemiconductor structure of FIG. 7 after forming additional block maskmaterial, patterning the additional block mask material to provide asecond block mask 28′, and performing a second metal gate treatment onthe physically exposed first modified TiN layer 30 in the pFET deviceregion 102 so as to provide a second modified TiN layer 34.

The forming of the additional block mask includes depositing additionalblock mask material in both device regions (100/102). The additionalblock mask material may include one of the block mask materialsmentioned above for block mask 28. In some embodiments, a hard maskmaterial can be formed on the additional block mask material prior topatterning and during the patterning process, hard mask 32 is formed.The hard mask material that provides hard mask 32 may include one of thehard mask materials mentioned above for the hard mask layer 14L. Thehard mask material that provides the hard mask 32 can be formedutilizing one of the deposited processes mentioned above for forminghard mask layer 14L. The hard mask 32 may have a thickness from 50 nm to100 nm.

The patterning of the additional block mask material and, if present,the hard mask material, may include lithography and etching. Theresultant second block mask 28′ that is formed is present in the nFETdevice region 100 as well as the pFET device region 102. In the nFETdevice region 100, the entirety of the first modified TiN layer 30 iscovered. In the pFET device region 102, the second block mask 28′protects only a lower portion of the first modified TiN layer 30. Anupper portion of the first modified TiN layer 30 in the pFET deviceregion 102 is physically exposed.

The second modified TiN layer 34 that is formed has a third workfunctionvalue that is lower than the second workfunction value. In oneembodiment, the third workfunction value of the second modified TiNlayer 34 is from 4.4 eV to 4.7 eV. In accordance with the presentapplication, the second modified TiN layer 34 has a threshold voltagethat is higher, i.e., greater, than the second threshold voltage and thefirst threshold voltage.

The second metal gate treatment includes introducing a threshold voltagemodifying dopant such as, for example, fluorine or oxygen into thephysically exposed portions of the first modified TiN layer 30 in thepFET device region 102. The threshold voltage modifying dopant may beintroduced into the physically exposed portions of the first modifiedTiN layer 30 in the pFET device region 102 utilizing a gas phase dopantprocess. The second block mask 28′ prevents any modification of then-type workfunction TiN liner 26L or the first modified TiN layer 30 inthe nFET device region. The second block mask 28′ also prevents anymodification of the protected/covered first modified TiN layer 30 in thepFET device region 102. The remaining first modified TiN layer 30 in thepFET device region 102 may be referred to as a first modified TiN liner30L.

In some embodiments, the concentration of threshold voltage modifyingdopant that is present in the second modified TiN layer 34 can be from1E20 atoms/cm³ to 8E21 atoms/cm³. Other concentrations of thresholdvoltage modifying dopant besides the range mentioned herein can bepresent in the second modified TiN layer 34 so as long as theconcentration of the threshold voltage modifying dopant that is presentin the second modified TiN layer 34 provides the desired thresholdvoltage change in the pFET device region.

Referring now to FIG. 9, there is illustrated the exemplarysemiconductor structure of FIG. 8 after recessing the second block mask28′, removing physically exposed portions of the first modified TiNlayer 30 in the nFET device region 100 and the second modified TiN layer34 in the pFET device region 102, and removing the gate dielectricmaterial layer 24 that is located beneath the physically exposedportions of the first modified TiN layer 30 and the physically exposedportions of the second modified TiN layer 34.

In some embodiments, and prior to recessing the second block mask 28′,the hard mask 32 is removed utilizing a material removal process suchas, for example, planarization or etching.

The second block mask 28′ may be recessed utilizing a recess etchingprocess that is selective in removing the block mask material. Theremaining second block mask 28′ after recessing may be referred to as arecessed block mask 28R. The recessed block mask 28R physically exposesa portion of the first modified TiN layer 30 in the nFET device region100, and a portion of the second modified TiN layer 34 in the pFETdevice region 102.

The physically exposed portion of the first modified TiN layer 30 in thenFET device region 100, and physically exposed portion of the secondmodified TiN layer 34 in the pFET device region 102 are removedutilizing an etching process that is selective in removing TiN. Aportions of the first modified TiN layer 30 remains in the nFET deviceregion 100, and a portion of the second modified TiN layer 34 remains inthe pFET device 102. The remaining portion of the first modified TiNlayer 30 is referred herein as a first modified TiN portion 30P, whilethe remaining portion of the second modified TiN layer 34 is referred toherein as a second modified TiN portion 34P.

The gate dielectric material layer 24 that is located beneath thephysically exposed portions of the first modified TiN layer 30 and thephysically exposed portions of the second modified TiN layer 34 may beremoved utilizing an etching process that is selective in removing thegate dielectric material. The remaining gate dielectric material layer24 may be referred to herein as a gate dielectric layer 24L. In someembodiments, a single etch may be used to remove the physically exposedportions of the modified TiN and underlying gate dielectric materiallayer in both device regions (100/102).

As is shown in FIG. 9, the removal of the physically exposed portions ofthe modified TiN and underlying gate dielectric material layer in bothdevice regions (100/102) physically exposes the hard mask caps 14 and anupper portion of each semiconductor fin 10F in both device regions(100/102).

Referring now to FIG. 10, there is illustrated the exemplarysemiconductor structure of FIG. 9 after removing the recessed block mask28R and subsequent formation of a gate encapsulation layer 36. Theremoval of the recessed block mask 28R may be performed utilizing anetching process that is selective in removing block mask material.

The gate encapsulation layer 36 is then formed. The gate encapsulationlayer 36 includes a hard mask material that may be the same as, ordifferent from, the hard mask material that provides the hard mask caps14. In one example, the gate encapsulation layer 36 may be composed ofsilicon nitride. The gate encapsulation layer 36 may be formed by adeposition process such as, for example, chemical vapor deposition (CVD)or plasma enhanced chemical vapor deposition (PECVD). The gateencapsulation layer 36 may have a thickness from 10 nm to 50 nm;although other thicknesses are possible and are not excluded from beingused.

Referring now to FIG. 11, there is illustrated the exemplarysemiconductor structure of FIG. 10 after formation of amiddle-of-the-line (MOL) dielectric material 40. The MOL dielectricmaterial 40 is formed on the gate encapsulation layer 36 and laterallysurrounds each of the semiconductor fins 10F. At this point of thepresent application, the MOL dielectric material 40 has a topmostsurface that is coplanar with a topmost surface of the gateencapsulation layer 36.

The MOL dielectric material 40 may be composed of, for example, silicondioxide, undoped silicate glass (USG), fluorosilicate glass (FSG),borophosphosilicate glass (BPSG), a spin-on low-k dielectric layer, achemical vapor deposition (CVD) low-k dielectric layer or anycombination thereof. The term “low-k” as used throughout the presentapplication denotes a dielectric material that has a dielectric constantof less than silicon dioxide. In another embodiment, a self-planarizingmaterial such as a spin-on glass (SOG) or a spin-on low-k dielectricmaterial such as SiLK™ can be used as the MOL dielectric material 40.The use of a self-planarizing dielectric material as the MOL dielectricmaterial 40 may avoid the need to perform a subsequent planarizing step.

In one embodiment, the MOL dielectric material 40 can be formedutilizing a deposition process including, for example, chemical vapordeposition (CVD), plasma enhanced chemical vapor deposition (PECVD),evaporation or spin-on coating. In some embodiments, a planarizationprocess and/or an etch back process follows the deposition of the MOLdielectric material 40.

Referring now to FIG. 12, there is illustrated he exemplarysemiconductor structure of FIG. 11 after exposing an uppermost portionof each semiconductor fin 10F in the nFET device region 100 and the pFETdevice region 100, and forming a top n-doped source/drain structure 42on the exposed surfaces of the semiconductor fins 10F in the nFET deviceregion 100 and a top p-doped source/drain structure 44 on the exposedsurfaces the semiconductor fins 10F in the pFET device region 102.

The exposing the uppermost portion of each semiconductor fin 10F in thenFET device region 100 and the pFET device region 100 includes firstrecessing an upper portion of the MOL dielectric material 40 utilizing arecess etching process. The remaining recessed MOL dielectric material40 may be referred to herein as a MOL dielectric structure 40S. Theheight of the MOL structure 40S should be higher than a topmost surfaceof the modified TiN portions (30P, 34P) in each of the device regions(100,102). The physically exposed portion of the gate encapsulationlayer is then removed utilizing a selective etch to provide a gateencapsulation liner 36L.

The gate encapsulation liner 36L is present on a sidewall surface and atopmost surface of the first modified TiN portion 30P and then-workfunction TiN liner 26L in the nFET device region 100, while thegate encapsulation liner 36L is present on a sidewall surface and atopmost surface of the second modified TiN portion 34P and the firstmodified TiN liner 30L in the pFET device region 102. Collectively, thefirst modified TiN portion 30P and the n-workfunction TiN liner 26L maybe referred to herein as an nFET gate structure having a gradientthreshold voltage (low to high), while the second modified TiN portion34P and the first modified TiN liner 30L in the pFET device region 102may be referred to herein as a pFET gate structure having a gradientthreshold voltage (low to high).

Each hard mask 14 is then removed utilizing a material removal processsuch as, for example, etching or planarization. In some embodiments, andwhen the gate encapsulation layer 36 and the hard masks 14 are composedof a same hard mask material, a portion of the hard masks 14 may beremoved during the etching of the gate encapsulation layer 36. At thispoint of the present application, an upper portion (sidewalls and atopmost surface) of each semiconductor fin 10F is physically exposed.

The top n-doped source/drain structure 42 and the top p-dopedsource/drain structure 44, which can be formed utilizing an epitaxialgrowth (or deposition) process, as defined above, can be formed in anyorder. For example, and in one embodiment, the top n-doped source/drainstructure 42 can be formed prior to the top p-doped source/drainstructure 44. In such an embodiment, a block mask is formed in the pFETdevice region 102 and then the top n-doped source/drain structure 42 isformed by epitaxial growth. Following the epitaxial growth of the topn-doped source/drain structure 42, the block mask is removed from thepFET device region 102, another block mask is formed in the nFET deviceregion 100 that now includes the top n-doped source/drain structure 42,and thereafter the top p-doped source/drain structure 44 is formed byepitaxial growth. Following epitaxial growth of the top p-dopedsource/drain structure 44, the another block mask is removed from thenFET device region 100. In embodiments, in which the top p-dopedsource/drain structure 44 is formed prior to the top n-dopedsource/drain structure 42, the order of the above mentioned processingsteps is reversed.

In accordance with the present application, the top n-doped source/drainstructure 42 and the top p-doped source/drain structure 44 are used as asource region of the vertical transport FETs.

The top n-doped source/drain structure 42 includes a semiconductormaterial and an n-type dopant. The semiconductor material that providesthe top nFET source/drain structure 42 may be the same or different fromthe semiconductor material of semiconductor substrate 10. Theconcentration of n-type dopant within the semiconductor material thatprovides the top n-doped source/drain structure 42 can range from 1×10¹⁸atoms/cm³ to 1×10²¹ atoms/cm³, although dopant concentrations greaterthan 1×10²¹ atoms/cm³ or less than 1×10¹⁸ atoms/cm³ are also conceived.The top n-doped source/drain structure 42 may be grown on exposedsidewalls and a topmost surface of each semiconductor fin 10F in thenFET device region 100. The top n-doped source/drain structure 42 mayhave a faceted surface. In one example, the top n-doped source/drainstructure 42 may be diamond shaped.

The top p-doped source/drain structure 44 includes a semiconductormaterial and a p-type dopant. The semiconductor material that providesthe top pFET source/drain structure 44 may be the same or different fromthe semiconductor material of semiconductor substrate 10. Also, thesemiconductor material that provides the top p-doped source/drainstructure 44 may be the same as, or different from, the semiconductormaterial that provides the top p-doped source/drain structure 42. Theconcentration of p-type dopant within the semiconductor material thatprovides the top p-doped source/drain structure 44 can range from 1×10¹⁸atoms/cm³ to 1×10²¹ atoms/cm³, although dopant concentrations greaterthan 1×10²¹ atoms/cm³ or less than 1×10¹⁸ atoms/cm³ are also conceived.The top p-doped source/drain structure 44 may be grown on exposedsidewalls and a topmost surface of each semiconductor fin 10F in thepFET device region 102. The top p-doped source/drain structure 44 mayhave a faceted surface. In one example, the top p-doped source/drainstructure 44 may be diamond shaped.

FIG. 12 illustrates an exemplary structure including a verticaltransport nFET and a laterally adjacent, but spaced apart, verticaltransport pFET. The vertical transport nFET includes at least onesemiconductor fin 10F present in an nFET device region 100 and extendingupwards from a surface of a base semiconductor substrate 10B. A bottomn-doped source/drain structure 18 is located on the base semiconductorsubstrate 10B and contacts sidewall surfaces of a lower portion of theat least one semiconductor fin 10F, wherein the bottom n-dopedsource/drain structure serves as a drain region. A gate dielectric layer24L is located above the bottom n-doped source/drain structure 18 andcontacts another portion of the sidewall surfaces of the at least onesemiconductor fin 10F. An nFET gate structure (26L, 30P) is locatedlaterally adjacent a sidewall of the gate dielectric layer 24L, the nFETgate structure (26L, 30P) comprises a TiN liner 26L having a firstthreshold voltage and a TiN portion 30P having a second thresholdvoltage that is greater than the first threshold voltage. As is shown, abottommost surface of TiN portion 30P directly contacts a topmostsurface of TiN liner 26L. A top n-doped source/drain structure 42 islocated on an upper portion of the at least one semiconductor fin 10Fand serves a source region.

The vertical transport pFET includes at least one semiconductor fin 10Fpresent in a pFET device region 102 and extending upwards from thesurface of the base semiconductor substrate 10B. A bottom p-dopedsource/drain structure 20 is located on the base semiconductor substrate10B and contacts sidewall surfaces of a lower portion of the at leastone semiconductor fin 10F, wherein the bottom p-doped source/drainstructure serves as a drain region. A gate dielectric layer 24L islocated above the bottom p-doped source/drain structure 20 and contactsanother portion of the sidewall surfaces of the at least onesemiconductor fin 10F. A pFET gate structure (30L, 34P) is locatedlaterally adjacent a sidewall of the gate dielectric layer 24L, the pFETgate structure (30L, 34P) comprises a TiN liner 30L having the secondthreshold voltage and a TiN portion 34P having a third threshold voltagethat is greater than the second threshold voltage. As is shown, abottommost surface of TiN portion 34P directly contacts a topmostsurface of TiN liner 30L. A top p-doped source/drain structure 44 islocated on an upper portion of the at least one semiconductor fin 10Fand serves as a source region.

Referring now to FIG. 13, there is illustrated the exemplarysemiconductor structure of FIG. 12 after forming a top spacer 46 and topsource/drain contact structures 50. The top spacer 46 is formed on thephysically exposed topmost surface of the MOL dielectric structure 40Sand on the physically exposed topmost surface of the gate encapsulationliner 36L.

The top spacer 46 may be composed of any dielectric spacer materialincluding for example, silicon dioxide, silicon nitride or siliconoxynitride. The top spacer 46 may be composed of a same, or different,dielectric spacer material than the bottom spacer 22. The top spacer 46may be formed utilizing a deposition process such as, for example,chemical vapor deposition or plasma enhanced chemical vapor deposition.In some instances, an etch may follow the deposition of the dielectricspacer material that provides the top spacer 46. The top spacer 46 mayhave a thickness from 4 nm to 10 nm. Other thicknesses that are lesserthan, or greater than, the aforementioned thickness range may also beemployed in the present application as the thickness of the top spacer46.

After top spacer 46 formation, an interlayer dielectric (ILD) material48 is formed. The ILD material 48 may include one of the dielectricmaterials mentioned above for the MOL dielectric material 40. The ILDmaterial 48 may include a same, or different dielectric material, thanthe MOL dielectric material 40. The ILD material 48 may be formed by oneof the deposition processes mentioned above in forming the MOLdielectric material 40. A planarization process may follow thedeposition of the dielectric material that provides the ILD material 48.

Contact openings (not specifically shown) are then formed into the ILDmaterial to physically exposed surfaces of the top n-doped source/drainstructure 42 and the top p-doped source/drain structure 44. A contactmetal such as, for example, copper, aluminum, tungsten, cobalt, oralloys thereof is the formed into each contact opening utilizing adeposition process. A planarization process may follow the depositionprocess. The contact metal or metal alloy within each contact opening isreferred to herein as a contact structure 50. As shown in FIG. 13, thecontact structures 50 have a topmost surface that is coplanar with atopmost surface of the ILD material 48.

While the present application has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present application. It is therefore intended that the presentapplication not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed is:
 1. A semiconductor structure comprising: a verticaltransport nFET and a laterally adjacent vertical transport pFET, whereinthe vertical transport nFET comprises: at least one semiconductor finpresent in an nFET device region and extending upwards from a surface ofa base semiconductor substrate; a bottom n-doped source/drain structurelocated on the base semiconductor substrate and contacting sidewallsurfaces of a lower portion of the at least one semiconductor fin,wherein the bottom n-doped source/drain structure serves as a drainregion; a gate dielectric layer located above the bottom n-dopedsource/drain structure and contacting another portion of the sidewallsurfaces of the at least one semiconductor fin; an nFET gate structurelocated laterally adjacent a sidewall of the gate dielectric layer, thenFET gate structure comprising a TiN liner having a first thresholdvoltage and a TiN portion having a second threshold voltage that isgreater than the first threshold voltage; and a top n-doped source/drainstructure located on an upper portion of the at least one semiconductorfin and serving a source region; and the vertical transport pFETcomprises: at least one semiconductor fin present in a pFET deviceregion and extending upwards from the surface of the base semiconductorsubstrate; a bottom p-doped source/drain structure located on the basesemiconductor substrate and contacting sidewall surfaces of a lowerportion of the at least one semiconductor fin, wherein the bottomp-doped source/drain structure serves as a drain region; a gatedielectric layer located above the bottom p-doped source/drain structureand contacting another portion of the sidewall surfaces of the at leastone semiconductor fin; a pFET gate structure located laterally adjacenta sidewall of the gate dielectric layer, the pFET gate structurecomprising a TiN liner having the second threshold voltage and a TiNportion having a third threshold voltage that is greater than the secondthreshold voltage; and a top p-doped source/drain structure located onan upper portion of the at least one semiconductor fin and serving as asource region.
 2. The semiconductor structure of claim 1, furthercomprising a gate encapsulation liner located on the nFET gate structureand the pFET gate structure.
 3. The semiconductor structure of claim 2,further comprising a MOL dielectric structure located adjacent the gateencapsulation liner.
 4. The semiconductor structure of claim 1, furthercomprising a bottom spacer located between the bottom n-dopedsource/drain structure and the gate dielectric layer in the nFET deviceregion and between the bottom p-doped source/drain structure and thegate dielectric layer in the pFET device region.
 5. The semiconductorstructure of claim 4, further comprising a top spacer located on the MOLdielectric structure.
 6. The semiconductor structure of claim 1, furthercomprising contact structures contacting surfaces of the top n-dopedsource/drain structure and the top p-doped source/drain structure. 7.The semiconductor structure of claim 1, further comprising an isolationstructure located between the vertical transport nFET and the verticaltransport pFET, wherein the isolation structure has a topmost surfacethat is coplanar with a topmost surface of bottom n-doped source/drainstructure and a topmost surface of the bottom p-doped source/drainstructure.
 8. The semiconductor structure of claim 1, wherein the leastone semiconductor fin present in the nFET device region has a sameheight as the least one semiconductor fin present in the pFET deviceregion.
 9. The semiconductor structure of claim 1, wherein the firstthreshold voltage of the TiN liner in the nFET device region is from 4.3eV to 4.6 eV and the second threshold voltage of the TiN portion in thenFET device region is from 4.6 eV to 4.9 eV.
 10. The semiconductorstructure of claim 9, wherein the second threshold voltage of the TiNliner in the pFET device region is from 4.6 eV to 4.9 eV and the thirdthreshold voltage of the TiN portion in the pFET device region is from4.4 eV to 4.7 eV.
 11. The semiconductor structure of claim 1, whereinthe TiN portion having the second threshold voltage in the nFET deviceregion and the TiN liner in the pFET device region are composed of TiNthat contains a threshold voltage modifying dopant in a dopantconcentration of from 1.5E20 atoms/cm³ to 8E21 atoms/cm³.
 12. Thesemiconductor structure of claim 11, wherein the threshold voltagemodifying dopant is fluorine or oxygen.
 13. The semiconductor structureof claim 1, wherein the TiN portion having the third threshold voltagein the pFET device region is composed of TiN that includes a thresholdvoltage modifying dopant in a dopant concentration from 1.E20 atoms/cm³to 8E21 atoms/cm³.
 14. The semiconductor structure of claim 13, whereinthe threshold voltage modifying dopant is fluorine or oxygen.
 15. Thesemiconductor structure of claim 5, further comprising an interlayerdielectric material located on the MOL dielectric structure.
 16. Thesemiconductor structure of claim 15, further comprising a first contactstructure located in the interlayer dielectric material and contacting asurface of the top n-doped source/drain structure, and a second contactstructure located in the interlayer dielectric material and contacting asurface of the top p-doped source/drain structure.
 17. The semiconductorstructure of claim 1, wherein the top n-doped source/drain structure hasa faceted shape and the top p-doped source/drain structure has a facetedshape.
 18. The semiconductor structure of claim 1, wherein the topn-doped source/drain structure has a diamond shape and the top p-dopedsource/drain structure has a diamond shape.
 19. The semiconductorstructure of claim 1, wherein the top n-doped source/drain structurecontacts a topmost surface and a sidewall surface of the least onesemiconductor fin present in the nFET device region, and the top p-dopedsource/drain structure contacts a topmost surface and a sidewall surfaceof the least one semiconductor fin present in the pFET device region.20. The semiconductor structure of claim 9, wherein the TiN liner in thenFET device region is composed entirely of TiN.